1. Field of Invention
This invention relates to motor-driven staple machines, and more particularly to a portable motor-driven staple machine used for joining building materials.
2. Description of Prior Art
A conventional motor-driven staple machine used for interior finishing work of buildings or the like is designed as follows: The elastic force of a spring is utilized to cause a staple driver to drive staples into a given object. The staple driver is coupled to a plunger. A compression spring is engaged with the plunger to urge the latter in the staple discharge direction. The plunger is raised through a cam mechanism by an electric motor, and the cam is disengaged from the plunger near the top dead center. As a result, the staple drive is abruptly moved downwardly by the elastic force of the compression spring, to drive the staple into the object such as a building material.
The motor has a start switch mechanism which is such that the trigger lever and the contact-detecting contact arm provided near the staple shot outlet form a mechanical AND mechanism for preventing staples from being carelessly discharged, and an automatic switch interrupting mechanism using a cam is provided to interrupt the application of power every operation cycle. In other words, the contact arm is pushed inwardly by abutting the shot outlet of the staple machine against the object, and the trigger lever is pulled to start the motor to cause the staple driver to drive a staple into the object. Thereafter, the plunger is raised to the standby position near the top dead center, and the power switch is turned off by the cam mechanism. Thus, the one operation cycle has been accomplished. The above-described staple driving operation is carried out repeatedly to drive a number of staples into the object or objects.
In the conventional motor-driven staple machine, the trigger lever and the contact arm form the mechanical AND mechanism, as described above. Hence, when only the trigger lever is operated, the motor is not started; that is, in order to discharge the staple, it is necessary to perform two different operations; i.e., to push the staple machine against a given object and then to operate the trigger lever. This is to prevent the accident that staples are carelessly discharged. However, for instance when the staple machine is moved by the operator, the following accident may occur: That is, with the trigger lever pulled, the contact arm may be set on a human body or the like. In this case, the motor is started to discharge the staple to cause bodily injury.
With the staple machine, the power is interrupted every operation cycle to suspend the staple driving operation; that is, it is necessary to operate the trigger lever for every staple. Therefore, when it is required to drive a number of staples continuously, it is rather troublesome to operate the trigger lever for every staple.
Thus, it is necessary to eliminate the above-described difficulty that staples may be carelessly discharged; i.e., to improve the safety of the staple machine, and to improve the operating performance of the staple machine thereby to enhance its work efficiency. However, there are technical problems which must be solved to satisfy those requirements. An object of the invention is to solve those technical problems.